Four gases were combined in a gas cylinder with these partial pressures: 3.5 atm n2, 2.8 atm o2, 0.25 atm ar, and 0.15 atm he. what is the total pressure inside the cylinder? what is the mole fraction of o2 and ar?

The total pressure is 6.7 atm.  The mole fractions of O₂ and Ar are 0.42 and 0.037.

p(Tot) = p(N₂) + p(O₂) + p(Ar) + p(He) = 3.5 atm + 2.8 atm + 0.25 atm + 0.15 atm = 6.7 atm

χ(O₂) = p(O₂)/p(Tot) = 2.8 atm/6.7 atm = 0.42

χ(Ar) = p(Ar)/p(Tot) = 0.25 atm/6.7 atm = 0.037